U.S. patent number 6,043,957 [Application Number 09/045,851] was granted by the patent office on 2000-03-28 for head positioning mechanism for magnetic disk device provided with micro tracking actuator using magnetic force and drive control method therefor.
This patent grant is currently assigned to NEC Corporation. Invention is credited to Toshiro Hattori, Hiroshi Kajitani, Masatomo Mizuta, Yoshiho Yanagita.
United States Patent |
6,043,957 |
Hattori , et al. |
March 28, 2000 |
**Please see images for:
( Certificate of Correction ) ** |
Head positioning mechanism for magnetic disk device provided with
micro tracking actuator using magnetic force and drive control
method therefor
Abstract
In a head positioning mechanism has a micro tracking actuator
which is between a carriage and a supporting spring for making the
supporting spring be rotated relative to the carriage to adjust a
position of a magnetic head, the micro tracking actuator has a pair
of coils held to one of said carriage and said supporting spring.
Each of the coils generates magnetic flux in response to a flow of
electric current therein. The micro tracking actuator further has a
magnet arrangement held to another of the carriage and the
supporting spring to face the coil means in a predetermined
direction. The magnet arrangement traverses the magnetic flux to
have a particular size which varies in accordance with a
predetermined relation in response to a relative movement between
the coils and the magnet arrangement. The carriage is movably
mounted to a magnetic disk device to which the head positioning
mechanism applied. The supporting spring is attached to the
carriage and rotatable around a predetermined axis extending in the
predetermined direction. The supporting spring holds the magnetic
head to perform a seeking operation of the magnetic head in
cooperation with the carriage.
Inventors: |
Hattori; Toshiro (Tokyo,
JP), Kajitani; Hiroshi (Tokyo, JP), Mizuta;
Masatomo (Tokyo, JP), Yanagita; Yoshiho (Tokyo,
JP) |
Assignee: |
NEC Corporation (Tokyo,
JP)
|
Family
ID: |
13360652 |
Appl.
No.: |
09/045,851 |
Filed: |
March 23, 1998 |
Foreign Application Priority Data
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Mar 21, 1997 [JP] |
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9-067980 |
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Current U.S.
Class: |
360/294.3;
360/294.6; G9B/5.193 |
Current CPC
Class: |
G11B
5/5552 (20130101) |
Current International
Class: |
G11B
5/55 (20060101); G11B 005/55 (); G11B 005/56 () |
Field of
Search: |
;360/105,106,109
;310/13 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2263369 |
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Oct 1990 |
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JP |
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4232678 |
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Aug 1992 |
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JP |
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Primary Examiner: Renner; Craig A.
Assistant Examiner: Castro; Angel
Attorney, Agent or Firm: Sughrue, Mion, Zinn Macpeak &
Seas, PLLC
Claims
What is claimed is:
1. A head positioning mechanism for a magnetic disk device, said
head positioning mechanism being for positioning a magnetic head on
a magnetic disk set to said magnetic disk device and
comprising:
a carriage movably mounted to said magnetic disk device;
a supporting spring attached to said carriage and rotatable around
a predetermined axis extending in a predetermined direction, said
supporting spring holding said magnetic head to perform a seeking
operation of said magnetic head in cooperation with said carriage;
and
a micro tracking actuator between said carriage and said supporting
spring for making said supporting spring be rotated relative to
said carriage to adjust a position of said magnetic head,
said micro tracking actuator comprising:
coil means held to one of said carriage and said supporting spring
for generating magnetic flux in response to a flow of electric
current therein; and
magnet means held to another of said carriage and said supporting
spring to face said coil means in said predetermined direction,
said magnet means traversing said magnetic flux and having a
plurality of independent segments lying in the same plane, wherein
at least one of said independent segments varies in size
substantially along its entirety in a direction of relative
movement between said coil means and said magnet means.
2. A head positioning mechanism as claimed in claim 1, wherein said
size varies proportionally to said relative movement.
3. A head positioning mechanism as claimed in claim 1, wherein said
micro tracking actuator further comprises:
a mounting member connected to said supporting spring for mounting
one of said coil means and said magnet means;
a stator shaft connected to said mounting member and extending
along said predetermined axis; and
hole defining means connected to said carriage and defining a
through hole in which said stator shaft is rotatably inserted.
4. A head positioning mechanism as claimed in claim 1, wherein said
coil means comprises a pair of coils which are arranged symmetrical
with respect to a first plane including said predetermined
axis.
5. A head positioning mechanism as claimed in claim 4, wherein said
magnet means comprises a pair of magnets which are arranged
symmetrical with respect to said first plane and face said coils,
respectively.
6. A head positioning mechanism as claimed in claim 5, wherein each
of said magnets has a trapezoidal shape in a second plane
intersecting rectangular to said predetermined axis.
7. A head positioning mechanism as claimed in claim 4, wherein said
magnet means comprises:
two inner magnets placed in such a manner as to adjoin at a center
therebetween; and
two outer magnets placed outside said inner magnets by being apart
from said inner magnets by a predetermined distance, respectively,
said two inner magnets having trapezoidal sections and having
magnetic poles at lower base sides thereof and being placed in such
a manner as to be symmetrical with respect to said first plane so
that lower base sides thereof face each other.
8. A head positioning mechanism as claimed in claim 4, wherein said
magnet means comprises:
two inner magnets placed in such a manner as to adjoin at a center
therebetween; and
two outer magnets placed outside said inner magnets by being apart
from said inner magnets by a predetermined distance, respectively,
said two inner magnets having trapezoidal sections and having
magnetic poles at lower base sides thereof and being placed in such
a manner as to be symmetrical with respect to said first plane so
that lower base sides thereof face each other, said two outer
magnets having trapezoidal sections and being placed outside said
two inner magnets by being apart from said two inner magnets by a
predetermined distance, respectively.
9. A head positioning mechanism as claimed in claim 4, wherein said
magnet means comprises:
two inner magnets placed in such a manner as to adjoin at a center
therebetween;; and
two outer magnets placed outside said inner magnets by being apart
from said inner magnets by a predetermined distance, respectively,
said two inner magnets having trapezoidal sections and having
magnetic poles at lower base sides thereof and being placed in such
a manner as to be axially symmetrical with respect to the movement
direction so that lower base sides thereof face each other, said
two outer magnets having rectangular sections and being placed
outside said two inner magnets by being apart form said two inner
magnets by a predetermined distance, respectively.
10. A head positioning mechanism as claimed in claim 4, wherein
said magnet means comprises:
two inner magnets placed in such a manner as to adjoin at a center
therebetween; and
two outer magnets placed outside said inner magnets by being apart
from said inner magnets by a predetermined distance, respectively,
said two inner magnets having rectangular sections and having
magnetic poles at lower base sides thereof and being placed in such
a manner as to be axially symmetrical with respect to the movement
direction so that lower base sides thereof face each other, said
two outer magnets having trapezoidal sections and being placed
outside said two inner, magnets by being apart from said two inner
magnets by a predetermined distance, respectively.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to a head positioning
mechanism for a magnetic disk device provided with a micro tracking
actuator which uses a magnetic force, and to a drive control method
therefor. More particularly, the present invention relates to a
head positioning mechanism for use in a magnetic disk device, which
is used for precisely fixing the positional relation between a
carriage and a supporting spring when performing a seeking
operation of moving a magnetic head to a target track of a magnetic
disk medium (hereunder referred to as a magnetic disk), and to a
drive control method therefor.
In the case of a conventional magnetic disk device, a seeking
operation of moving a magnetic head to a target track of a magnetic
disk is performed by an actuator. The magnetic head is moved to a
target track in a control mode. Further, the conventional magnetic
disk device is adapted so that the magnetic head is held on the
target track in a position control mode after the magnetic head
reaches the target track.
In the case of such a conventional magnetic disk device, the
movement of a magnetic head is performed by using a carriage and a
supporting spring which are connected to an actuator. However,
recently, as the storage capacity of a magnetic disk is
considerably increased, an actuator is required to have high
accuracy of positioning of a magnetic head. To enhance the accuracy
of positioning of a magnetic head, there has been proposed a system
which uses a micro tracking actuator for performing a seeking
operation of moving a magnetic head by a minute distance.
For example, a magnetic disk device employing a minute displacement
generating element as the micro tracking actuator has been known as
such a conventional system. In the case of this conventional
system, when performing a (high-precision) seeking operation of
moving a magnetic head to a target track of a magnetic head, a
(coarse) seeking operation of moving the magnetic head to the
target track is first performed. Then, the actuator is stopped.
Subsequently, the positioning of the magnetic head by means of the
minute displacement generating element according to a position
error signal is performed as a precise seeking operation of moving
the magnetic head.
Moreover, there has been another conventional magnetic disk device
provided with a micro tracking actuator using a magnetic force.
This magnetic disk device is provided with a carriage and a
supporting spring.
However, in the case of the former magnetic disk device using the
minute displacement element, a high voltage is necessary for
driving the element. Further, the minute displacement generating
element has drawbacks in that the long-term reliability thereof is
low and thus, the practicality thereof is low.
Furthermore, in the latter case, namely, in the case of the micro
tracking actuator using a magnetic force, the supporting spring is
vibrated owing to the seeking operation. Thus, such a micro
tracking actuator has a drawback in that it is difficult to achieve
the complete fixation thereof.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a
head positioning mechanism for a magnetic disk device, which can
perform the functions of the conventional micro tracking actuator
by employing a physically single configuration, and to provide a
drive control method therefor.
Further, another object of the present invention is to provide a
head positioning mechanism for a magnetic disk device, by which a
reduction in size of the head positioning mechanism is achieved,
and to provide a drive control method therefor.
Moreover, still another object of the present invention is to
provide a head positioning mechanism for a magnetic disk device, by
which a position control operation can be easily performed, and to
provide a drive control method therefor.
According to an aspect of this invention, there is provided a head
positioning mechanism for a magnetic disk device. The head
positioning mechanism is for positioning a magnetic head on a
magnetic disk set to the magnetic disk device and comprises a
carriage movably mounted to the magnetic disk device and a
supporting spring attached to the carriage and rotatable around a
predetermined axis extending in a predetermined direction. The
supporting spring holds the magnetic head to perform a seeking
operation of the magnetic head in cooperation with the carriage.
The head positioning mechanism further comprises a micro tracking
actuator between the carriage and the supporting spring for making
the supporting spring be rotated relative to the carriage to adjust
a position of the magnetic head. In the head positioning mechanism,
the micro tracking actuator comprises coil means held to one of the
carriage and the supporting spring for generating magnetic flux in
response to a flow of electric current therein and magnet means
held to another of the carriage and the supporting spring to face
the coil means in the predetermined direction. The magnet means
traverses the magnetic flux to have a particular size which varies
in accordance with a predetermined relation in response to a
relative movement between the coil means and the magnet means.
According to another aspect of this invention, there is provided a
head positioning mechanism for a magnetic disk device. The head
positioning mechanism is for positioning a magnetic head on a
magnetic disk set to the magnetic disk device and comprises a
carriage movably mounted to the magnetic disk device and a
supporting spring attached to the carriage and rotatable around a
predetermined axis extending in a predetermined direction. The
supporting spring holds the magnetic head to perform a seeking
operation of the magnetic head in cooperation with the carriage.
The head positioning mechanism further comprises a micro tracking
actuator between the carriage and the supporting spring for making
the supporting spring be rotated relative to the carriage to adjust
a position of the magnetic head. In the head positioning mechanism,
the micro tracking actuator comprises a pair of coils held to one
of the carriage and the supporting spring for generating magnetic
flux in response to a flow of electric current therein and magnet
means held to another of the carriage and the supporting spring to
face the coils in the predetermined direction.
According to still another aspect of this invention, there is
provided a drive control method of driving a head positioning
mechanism for a magnetic disk device. The head positioning
mechanism is for positioning a magnetic head on a magnetic disk set
to the magnetic disk device and comprises a carriage movably
mounted to the magnetic disk device and a supporting spring
attached to the carriage and rotatable around a predetermined axis
extending in a predetermined direction. The supporting spring holds
the magnetic head to perform a seeking operation of the magnetic
head in cooperation with the carriage. The head positioning
mechanism further comprises a micro tracking actuator between the
carriage and the supporting spring for making the supporting spring
be rotated relative to the carriage to adjust a position of the
magnetic head. The micro tracking actuator comprises a pair of
coils held to one of the carriage and the supporting spring each
for generating magnetic flux in response to an electric current
therein and magnet means held to another of the carriage and the
supporting spring to face the coils in the predetermined direction.
The drive control method comprises the steps of supplying, during
movement of the carriage, the electric current to the coils in
reverse to prevent the supporting spring from being rotated
relative to the carriage and supplying, during a stop of the
carriage, the electric current to the coils in a same direction to
move the supporting spring relative to the carriage.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features, objects and advantages of the present invention
will become apparent from the following description of preferred
embodiments with reference to the drawings in which like reference
characters designate like or corresponding parts throughout several
views, and in which:
FIG. 1 is a perspective diagram showing a conventional
actuator;
FIG. 2 is an exploded perspective diagram showing a conventional
micro tracking actuator;
FIG. 3 is an exploded perspective diagram showing an example of a
head positioning mechanism for a magnetic disk device, which has a
micro tracking actuator of the present invention;
FIG. 4 is a diagram schematically illustrating the configuration of
a magnetic disk device to which the example of the head positioning
mechanism for the magnetic disk device according to the present
invention is applied;
FIG. 5 is a partially sectional diagram showing the configuration
of and the connection state between a carriage and a supporting
spring that are illustrated in FIG. 1;
FIG. 6 is a diagram showing the configuration of a primary part of
a first embodiment of the head positioning mechanism of the present
invention;
FIG. 7 is a diagram showing the configuration of a primary part of
a second embodiment of the head positioning mechanism of the
present invention;
FIG. 8 is a diagram showing the configuration of a primary part of
a third embodiment of the head positioning mechanism of the present
invention;
FIG. 9 is a diagram showing the configuration of a primary part of
a fourth embodiment of the head positioning mechanism of the
present invention;
FIG. 10 is a diagram showing the configuration of a primary part of
a fifth embodiment of the head positioning mechanism of the present
invention;
FIG. 11 is a diagram showing the configuration of a primary part of
a sixth embodiment of the head positioning mechanism of the present
invention;
FIG. 12 is a diagram showing the configuration of a primary part of
a seventh embodiment of the head positioning mechanism of the
present invention;
FIG. 13 is a diagram showing the configuration of a primary part of
an eighth embodiment of the head positioning mechanism of the
present invention;
FIG. 14 is a graph illustrating the relation between the amount of
movement of a coil and the length of a part of the coil traversing
(or cutting across) magnetic flux (lines);
FIG. 15 is a graph illustrating the relation among the amount of
movement of a coil, the length of a part of the coil traversing
magnetic flux (lines) and the driving force exerted on the
coil;
FIGS. 16 and 17 are diagrams each illustrating an operation of the
micro tracking actuator; and
FIGS. 18 and 19 are diagrams each illustrating an operation of
accessing a magnetic disk medium.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before describing the preferred embodiments of the present
invention, a conventional actuator will be specifically described
hereinbelow, for the reader's better understanding of the present
invention, by referring to FIG. 1.
As illustrated in FIG. 1, a conventional magnetic device has: a
carriage 2 connected to a main actuator 1; a supporting spring 3
connected with this carriage 2; and a magnetic head 4 provided at a
tip end portion of the supporting spring 3.
The main actuator 1 causes the magnetic head 4 to perform a seeking
operation of moving to a target track on a magnetic disk.
Meanwhile, as the storage density of a magnetic disk is
considerably increased, the enhancement of the accuracy of
positioning of the magnetic head 4 to a target track becomes a
serious problem. It is, however, difficult to adapt the
aforementioned magnetic disk device to the situation in which the
storage density of a magnetic disk is considerably increased.
Therefore, there has been proposed a system which employs a micro
tracking actuator (namely, a micro actuator) for moving each
magnetic head 4 by a minute distance so as to enhance the accuracy
of positioning of the magnetic head 4, aside from the main actuator
1.
For example, magnetic disk devices, each of which employs a minute
displacement generating element as a micro tracking actuator, are
disclosed in Japanese Unexamined Patent Publication Nos. 2-263369
and 4-232678 Official Gazettes, as prior art systems.
In the case that a seeking operation of moving a magnetic head to a
target track of a magnetic disk is performed in each of these prior
art systems, the (coarse) seeking operation of moving the magnetic
head to the target track of the magnetic disk is performed by using
the main actuator. During this seeking operation, the main actuator
is at a standstill. Upon completion of the seeking operation of
moving the magnetic head, the main actuator is stopped.
Subsequently, a (fine or precise) seeking operation for precisely
positioning the magnetic head is performed according to a position
error signal as the next operation by using the minute displacement
generating element.
Further, a magnetic disk device employing a micro tracking actuator
of the high compliance type, which uses a magnetic force, is
disclosed in Proceedings of the JSME (Japan Society of Mechanical
Engineers) IIP (Information/Intelligence/Precision Instrument)
Conference, 1996 (Proc. JSME IIP Conf. '96).
FIG. 2 shows the piggyback actuator structure of a micro tracking
actuator. Yoke 22 and a magnet 23 are fixed to a carriage 21.
Further, a coil 27 is fixed to a moving (or movable) portion 25 in
such a manner as to face the magnet 23. Moreover, a supporting
spring 24 is fixed to the moving portion 25 at a side opposite to
this coil 27. Magnetic head 26 is provided at a tip end of the
supporting spring 24. Furthermore, a cross-shaped (or X-shaped)
spring 28 is provided on the moving portion 25. Bending of this
cross-shaped spring 28 results in a swinging motion of the moving
portion 25 around a stator shaft 29 fixed to the carriage 21.
However, as above described, the conventional micro tracking
actuators respectively using the minute displacement generating
element and the magnetic force have the drawbacks in that the
practicality thereof is low and that the supporting spring vibrates
owing to the seeking operation.
Hereinafter, the preferred embodiments of the head positioning
mechanism for the magnetic disk device according to the present
invention, and of the drive control method therefor will be
described by referring to the accompanying drawings. FIG. 3 shows a
head positioning mechanism of a magnetic disk device, which is
provided with a micro tracking actuator.
Referring to FIG. 3, there is shown the head positioning mechanism
for the magnetic disk device, which comprises a main actuator (or
rotary actuator) 31, a carriage 32 connected to this main actuator
31; a supporting spring 35, a magnetic head 37 held at an end part
of the supporting spring through a slider 36, a mounting member 39
connecting with the other end part of the supporting member 35, a
stator shaft 41 provided on the mounting member 39 and having a
predetermined axis extending in a predetermined direction, a
plurality of coil supporting portions 43a, 43b and 43c connected to
the mounting member 39 on a side opposite to the supporting spring
35, and first and second coils 50 and 51 respectively provided
between the coil supporting portions 43b and 43c and between the
coil supporting portions 43a and 43b.
Stator shaft frame 61 is provided at an end part of the carriage
32. Through hole 61a, into which the stator shaft 41 is rotatably
fitted, is formed in the stator shaft frame 61. Moreover, a
magnetic circuit 63 is provided in the carriage 32 in the rear of
the stator shaft frame 61.
The first and second coils 50 and 51 have same magnetic
characteristics and are equipped between the coil supporting
portions 43b and 43c and between the coil supporting portions 43a
and 43b, respectively. These first and second coils 50 and 51 are
equipped therebetween in such a way as to face the carriage 32.
Further, the magnetic circuit 63 is equipped in the carriage 32 in
such a manner as to face the first and second coils 50 and 51.
Incidentally, the first and second coils 50 and 51 and the magnetic
circuit 63 operate as VCM (Voice Coil Motor).
Supporting coil 35 supports the magnetic head 37 on a surface of a
magnetic disk 47 (see FIG. 4) in such a manner as to face this
surface of the magnetic disk 47. Stator shaft 41 is fitted into the
through hole 61a in such a manner that the supporting spring 35 can
rotate along the surface of the magnetic disk 47. Carriage 32 has
the other end portion connected to the main actuator 31 and rotates
along the surface of the magnetic disk 47 together with the
supporting spring 35.
Magnetic head 37 is attached to the slider 36 which serves a
function of causing the magnetic head 37 to rise from the surface
of the magnetic disk 47 and to float thereabove. This slider 36 is
supported by the supporting spring 35. Mounting member 39 and the
carriage 32 are rotatably coupled to each other by the stator shaft
41 and the stator shaft frame 61.
FIG. 4 shows a magnetic disk device to which the embodiment of the
head positioning mechanism for the magnetic disk device according
to the present invention is applied. Device of FIG. 4 will be
described hereunder by assuming the presence of a plurality of
magnetic disks 37 and a plurality of magnetic heads 47.
Incidentally, this magnetic disk device may have only one magnetic
disk 47 and only one magnetic head 37.
Referring to FIG. 4, the plurality of magnetic disks 47 disposed by
being spaced out are rotatably held by a spindle 71. Each of the
magnetic disks 47 is adapted so that data recorded on both surfaces
thereof are read by the corresponding magnetic head 37.
As shown in FIG. 5, a plurality of magnets 65a, 65b, 65c and 65d
(incidentally, four magnets are shown in FIG. 6) and a yoke 67,
which serve as a magnet arrangement or a magnetic circuit 63, are
provided on the carriage 32. First and second coils 50 and 51 are
respectively equipped at places, which face the magnets 65a, 65b,
65c and 65d and the yoke 67 in the predetermined direction. As is
apparent from FIG. 5, the magnets 65a, 65b, 65c and 65d directly
face the first and second coils 50 and 51 by establishing a
predetermined space between the magnets and the coils. Yoke 67 is
provided on the magnets 65a, 65b, 65c and 65d. It is noted here
that the magnets 65a-65d are arranged symmetrical with respect to a
first plane including the predetermined axis and that each of the
magnets 65a-65d has one of a trapezoidal shape and a rectangular
shape in a second plane intersecting perpendicular to the
predetermined axis.
Micro tracking actuator is composed of the first and second coils
50 and 51 and the magnetic circuit 63, the stator shaft 41 and the
stator shaft frame 61. In the case of using this micro tracking
actuator, the magnetic head 37 is adapted to move by a minute
distance as the supporting spring 35 rotates.
Magnets 65a, 65b, 65c and 65d mounted on the carriage 32 are shown
concretely as first to eighth embodiments in FIGS. 6 to 13.
Further, the magnets 65a, 65b, 65c and 65d mounted on the carriage
32 are placed along a direction, in which the first and second
coils 50 and 51 move, and are disposed in such a way as to be
axially symmetrical with respect to an axis of symmetry VI shown in
FIG. 6. Incidentally, the axis of symmetry VI is a center virtual
axis passing through a portion between the first and second coils
50 and 51. Additionally, the axis of symmetry VI is on a line
passing through the shaft center of the stator shaft 41 and the
coil supporting portion 43b located at the central part of the
carriage 32. Namely, the first and second coils 50 and 51 and the
magnets 65a, 65b, 65c and 65d are disposed in such a way as to be
axially symmetrical with respect to the common axis of symmetry
VI.
Further, magnets having shapes, by which the amounts x1, x2 and x3
of relative movement of each of the first and second coils 50 and
51 is proportional to variation in the length L1, L2, L3 of a part
of each of the coils 50 and 51 traversing magnetic flux as
illustrated in FIGS. 14 and 15, are used as the magnets 65a, 65b,
65c and 65d. That is, the magnet arrangement traverse the magnetic
flux to have a particular size which varies in accordance with a
predetermined relation in response to a relative movement between
the coils and the magnet arrangement.
Hereunder, the lengths L1, L2, L3 of a part, which traverses the
magnetic flux, of each of the coils 50 and 51 will be described.
For instance, regarding the outermost periphery line of the coil
having several turns, the lengths L1, L2 and L3 of the part
traversing the magnetic flux generated by the magnet 65c of FIG. 14
are the lengths L1, L2 and L3 of a part, which traverses the
magnetic flux and corresponds to the position of the first coil 50,
of one turn thereof. Hereinafter, each of "the lengths L1, L2 and
L3 of a part, which traverses the magnetic flux, of each of the
coils 50 and 51" designates a sum of the length L1, L2 or L3 of
corresponding parts (namely, parts corresponding to the part of the
outermost periphery of the coil 50 or 51) of the turns of the coil
50 or 51.
In the case of employing this shape of the magnet 65c, each of the
lengths L1, L2 and L3 of a part, which traverses the magnetic flux,
of each of the coils 50 and 51 varies owing to a change in the
relative positions of the supporting spring 35 and the carriage 32.
Further, the driving force F1, F2, F3 exerted on each of the first
and second coils 50 and 51 varies in such a way as to be
proportional to the amount x1, x2, x3 of relative movement of each
of the first and second coils 50 and 51 and to the amount of
variation in the length L1, L2, L3 of a part, which traverses the
magnetic flux, of each of the coils 50 and 51. For example, in the
case that the magnets 65a, 65b, 65c and 65d have the shapes as
shown in FIG. 16 (namely, the shapes similar to those of the
magnets of FIG. 6), when the first coil 50 moves to a side as
indicated by an arrow IX, the lengths L1, L2 and L3 of a part,
which traverses the magnetic flux, of the first coil 50
decrease.
This results in reduction in the force exerted on the first coil
50. In contrast, the lengths L1, L2 and L3 of a part, which
traverses the magnetic flux, of the second coil 51 increase. Thus,
the force exerted on the second d coil 51 increases. Conversely, as
shown in FIG. 17, when the second coil 51 moves to a side as
indicated by an arrow XI, the lengths L1, L2 and L3 of a part,
which traverses the magnetic flux, of the first coil 50 increase.
Thus, the force exerted on the first coil 50 increases. Further,
the lengths L1, L2 and L3 of a part, which traverses the magnetic
flux, of the second coil 51 decrease. Thus, the force exerted on
the second d coil 51 decreases. Then, in the case that equal
amounts of driving currents are made to flow through the first and
second coils 50 and 51 in such a manner that the driving forces are
applied to the coils 50 and 51 in opposite directions (namely, in
the case of this embodiment, inward directions), respectively, the
length of a part, which traverses the magnetic flux, of the second
coil 51 is different from the length of a part, which traverses the
magnetic flux, of the first coil 50. Moreover, the supporting
spring 35 is pushed back and fixed to the position of the axis of
symmetry IV for the magnets 65a, 65b, 65c and 65d owing to the
difference between the forces exerted on the magnets 65a, 65b, 65c,
65d in such a manner that the length of a part, which traverses the
magnetic flux, of the second coil 51 becomes equal to the length of
a part, which traverses the magnetic flux, of the first coil 50.
Holding force at that time is determined by a driving current value
I, a magnetic flux density B, an amount of movement of the coil x,
and the ratio k of the amount of variation in the length of a part,
which traverses the magnetic flux, of the coil to the amount of
movement of the coil as expressed by the following equation
(1):
Driving force:
I: Driving current value
B: Magnetic flux density
L: Length of a part, which traverses magnetic flux of each of the
coils, of each of the coils at the central position
.DELTA.L: an amount of variation in the length of a part, which
traverses magnetic flux, of each of the coils
x: an amount of movement of the coil from the center position
k (=.DELTA.L/x): a ratio k of the amount of variation in the length
of a part, which traverses the magnetic flux, of the coil to the
amount of movement of the coil
When driving currents are made to flow through the first and second
coils 50 and 51 so that driving forces, whose magnitudes are equal
to each other, are exerted thereon and the micro tracking actuator
is driven, a total length of parts, which traverse magnetic flux,
of the first and second coils 50 and 51 becomes constant as
regardless of the positions of the coils 50 and 51, as expressed by
the following equation (2). In the case of this magnetic disk
device, when the driving current value I is proportional to a force
applied to the micro tracking actuator, this actuator performs an
operation similar to that of the conventional micro tracking
actuator.
Driving force:
Hereinafter, the embodiments respectively having the different
configurations of the magnets 65a, 65b, 65c and 65d will be
described by referring to FIGS. 6 to 13. Incidentally, in each of
these embodiments respectively illustrated in these figures, each
of theses embodiments have magnetic poles in a direction (namely,
an upward or downward direction) in which these magnets move.
Incidentally, trapezoids employed as the shape of each of the four
magnets 65a, 65b, 65c and 65d are established so that the upper
base side thereof is parallel with the lower base side thereof.
Further, the upper base side thereof is shorter than the lower base
side. Moreover, hereunder, two magnets 65a and 65d will be referred
to as outer magnets. Furthermore, tow magnets 65b and 65c placed in
the inside of these outer magnets 65a and 65d will be referred to
as inner magnets.
In the case of the first embodiment illustrated in FIG. 6, each of
inner two magnets 65b and 65c adjoining with each other at the
center is formed like an axial symmetrical isosceles trapezoid in
such a manner that the upper base sides thereof are directed
inwardly. Namely, these magnets 65b and 65c are adjacent to each
other and are in contact with each other at the upper base side
thereof. Magnets having rectangular sections are placed in an
axially symmetrical manner as opposed outer two magnets 65a and 65d
facing each other in such a way as not to adjoin the two inner
magnets 65b and 65c. In this case, to fix the supporting spring 35
to the carriage 32, electric currents are fed through the coils 50
and 51 in such a manner that the driving force exerted on the inner
parts of the first and second coils 50 and 51 are attractive
forces.
Incidentally, a group of the two inner magnets 65b and 65c and
another group of the two outer magnets 65a and 65d are placed above
the first and second coils 50 and 51 so that these groups
simultaneously overlap the first and second coils 50 and 51,
respectively. This configuration is employed similarly in the
embodiments which will be described hereinbelow.
In the case of the second embodiment of FIG. 7, two inner magnets
65b and 65c are placed in such a way that the upper base sides of
these magnets are directed outwardly. Namely, these inner magnets
65b and 65c are placed in an axially symmetrical manner so that
these magnets 65b and 65c are adjacent to each other and are in
contact with each other at the lower base sides thereof. Two
rectangular magnets are disposed in an axially symmetrical manner
as the outer magnets 65a and 65d opposed in such a manner as not to
adjoin the two inner magnets 65b and 65c. To fix the supporting
spring 35 to the carriage 32, electric currents are fed through the
first and second coils 50 and 51 so that the driving force exerted
on the inner parts of the first and second coils 50 and 51 are
repulsive forces.
In the case of the third embodiment illustrated in FIG. 8,
rectangular adjacent magnets are placed in an axially symmetrical
manner as the two inner magnets 65b and 65c, respectively. Each of
two outer magnets 65a and 65d opposed in such a manner as not to
adjoin the inner magnets 65b and 65c, respectively, is shaped in
such a manner as to have a trapezoid section. Two outer magnets 65a
and 65d are opposed to each other in such a fashion that the upper
base sides of these outer magnets do not adjoin the two inner
magnets 65b and 65c, respectively. To fix the supporting spring 35
to the carriage 32, electric currents are fed through the coils 50
and 51 in such a manner that the driving force exerted on the outer
parts of the first and second coils 50 and 51 are attractive
forces.
In the case of the fourth embodiment illustrated in FIG. 9, magnets
having rectangular sections are used as the two inner magnets 65b
and 65c. Two outer magnets 65a and 65d are shaped so that the lower
base sides of these outer magnets face the magnets 65b and 65c,
respectively, and the outer magnets 65a and 65d has trapezoidal
sections. To fix the supporting spring 35 to the carriage 32,
electric currents are fed through the first and second coils 50 and
51 so that the driving force exerted on the outer parts of the
first and second coils 50 and 51 are repulsive forces.
In the case of the fifth embodiment shown in FIG. 10, opposed
magnets, which have trapezoidal sections so that the upper base
sides thereof adjoin each other, are used as the two inner magnets
65b and 65c. In contrast, the two outer magnets 65a and 65d are
magnets placed so that the upper base sides thereof are directed
outwardly. Namely, the two outer magnets 65a and 65d are placed so
that the lower base sides of these outer magnets face the two inner
magnets 65b and 65c, respectively. To fix the supporting spring 35
to the carriage 32, electric currents are fed through the first and
second coils 50 and 51 so that the driving force exerted on the
outer parts of the first and second coils 50 and 51 are repulsive
forces.
In the case of the sixth embodiment shown in FIG. 11, magnets,
which have trapezoidal sections, are used as the two inner magnets
65b and 65c. Two inner magnets 65b and 65c are placed in such a way
as to adjoin each other at the upper base sides thereof. Two outer
magnets 65a and 65d having trapezoidal sections are magnets placed
so that the upper base sides thereof are directed inwardly. Namely,
the two outer magnets 65a and 65d are placed so that the upper base
sides of these outer magnets face the two inner magnets 65b and
65c, respectively. To fix the supporting spring 35 to the carriage
32, electric currents are fed through the first and second coils 50
and 51 so that the driving force exerted on the inner parts of the
first and second coils 50 and 51 are attractive forces and that the
driving force exerted on the outer parts of the first and second
coils 50 and 51 are attractive forces.
In the case of the seventh embodiment of FIG. 12, all of two inner
magnets 65b and 65c and two outer magnets 65a and 65d are placed in
such a way that the upper base sides of these magnets have
trapezoidal sections and are directed outwardly. To fix the
supporting spring 35 to the carriage 32, electric currents are fed
through the first and second coils 50 and 51 so that the driving
force exerted on the inner parts of the first and second coils 50
and 51 are repulsive forces and that the driving force exerted on
the outer parts of the first and second coils 50 and 51 are
repulsive forces.
In the case of the eighth embodiment shown in FIG. 13, magnets,
which have trapezoidal sections, are used as the two inner magnets
65b and 65c. Magnets, which have trapezoidal sections and are
placed so that the upper base sides of these outer magnets are
directed inwardly, are used as two outer magnets 65a and 65d. To
fix the supporting spring 35 to the carriage 32, electric currents
are fed through the first and second coils 50 and 51 so that the
driving force exerted on the inner parts of the first and second
coils 50 and 51 are repulsive forces and that the driving force
exerted on the outer parts of the first and second coils 50 and 51
are attractive forces.
FIG. 14 shows variations in the lengths L1, L2 and L3 of parts
traversing magnetic flux corresponding to the outermost periphery
of each of the coils, which are caused by the movement of the first
coil 50 when the amounts x1, x2 and x3 of movement of each of the
coils of the minute tracking actuator are minute. Incidentally,
FIG. 14 illustrates the case, in which the two inner magnets 65b
and 65c have trapezoidal horizontal sections as in the first
embodiment shown in FIG. 6, by way of example.
Referring to FIG. 14, among the amounts x1, x2 and x3 of movement
of the first coil 50, the relation expressed by the following
equation (3) approximately holds when considering an arrow XX as an
axis of coordinate:
In FIG. 15, the axes of ordinate represent the length L1, L2 and L3
of the part, which traversing magnetic flux, of the first coil 50
and the driving force F1, F2, F3 exerted on the coil 50; and the
axis of abscissa represents the amount X1, X2, X3 of movement of
this coil. Incidentally, the proportional relation is established
between the amount x1, x2, x3 of movement of the coil and the
length L1, L2, L3 of the part, which traversing magnetic flux, of
the coil, as indicated by the line 81 of the graph of FIG. 15.
Thus, as is understood from the aforementioned equation (1), the
amount x1, x2, x3 of movement of the coil is proportional to the
driving force F1, F2, F3 applied to the coil as indicated by the
line 82 the graph of FIG. 15. This holds true for the other line
wound in such a manner as to form the coil having several turns.
Thus, the relations represented by the lines 81 and 82 of the graph
hold for the entire coils.
Hereinafter, based on the foregoing description, an operation of
the micro tracking actuator will be described by referring to FIGS.
16 and 17. Referring to FIGS. 16 and 17, the supporting spring 35
rotates with respect to the carriage 32. Thus, the relative
positions of the first and second coils 50 and 51 with respect to
the magnets 65a, 65b, 65c and 65d are changed. At that time, the
length of the part, which transverses the magnetic flux, of each of
the coils is changed. Further, as above described, the driving
forces respectively exerted on the first and second coils 50 and 51
vary. Accordingly, when driving currents are fed through the coils
50 and 51 so that driving forces, which have equal magnitude and
act in opposite directions, are generated in the first and second
coils 50 and 51, the magnitude of the driving force for driving the
second coil 51 becomes larger than that of the driving force for
driving the first coil 50 because the length of the part, which
traversing the magnetic flux, of the second coil 51 is longer than
that of the part, which traversing the magnetic flux, of the first
coil 50.
At that time, the micro tracking actuator rotates in a direction
from the second coil 51 to the fist coil 50, which is indicated by
an arrow XIII. Further, in the case illustrated in FIG. 17, the
magnitude of the driving force for driving the first coil 50
becomes larger than that of the driving force for driving the
second coil 51 because the length of the part, which traversing the
magnetic flux, of the first coil 50 is longer than that of the
part, which traversing the magnetic flux, of the second coil 51. At
that time, the micro tracking actuator rotates in a direction from
the first coil 50 to the second coil 51, namely, in a direction
indicated by an arrow XV.
As above described, in the state that the forces respectively
exerted on the first and second coils 50 and 51 do not balance with
each other, the micro tracking actuator rotates so that the length
of the part, which traversing the magnetic flux, of the first coil
50 is equal to that of the part, which traversing the magnetic
flux, of the second coil 51. For example, when the magnets 65a,
65b, 65c and 65d have trapezoidal horizontal sections and the
amount of movement of the minute tracking actuator is minute, the
amount of movement of the micro tracking actuator is proportional
to the amount in variation in the length of the part, which
traverses the magnetic flux, of the coil, as above stated.
Consequently, the amount of variation in the difference between the
lengths of the parts, which traverse the magnetic flux, of the
coils is proportional to the amount of movement of the micro
tracking actuator.
Moreover, because the vibration of the micro tracking actuator is
attenuated by a damping force such as a frictional force caused on
the stator shaft 41, the supporting spring 35 is fixed at a place
where the forces applied to the first and second coils 50 and 51
balance with each other, as illustrated in FIG. 6.
Moreover, when the magnets 65a, 65b, 65c and 65d have trapezoidal
horizontal sections and the amount of movement of the minute
tracking actuator is minute, the amount of movement of the micro
tracking actuator is proportional to the amount in variation in the
length of the part, which traverses the magnetic flux, of the coil,
as above described. Thus, the amount of variation in the difference
between the lengths of the parts, which traverse the magnetic flux,
of the first and second coils 50 and 51 is proportional to the
amount of movement of the micro tracking actuator. Furthermore,
because the vibration of the micro tracking actuator is attenuated
by a damping force such as a frictional force caused on the stator
shaft 41, the supporting spring 35 is fixed at a place where the
forces applied to the first and second coils 50 and 51 balance with
each other.
Thus, in the case that the supporting spring 35 vibrates without
having sufficient damping elements, there is the necessity for
providing a composing element, by which the vibration of the
supporting spring 35 is rapidly attenuated, on the stator shaft 41.
Such a composing element is required to connecting the stator shaft
41 with the stator shaft frame 61 by using, for instance,
rubber.
Further, as indicated by the equation (2), in the case that the
amount of movement of the micro tracking actuator is made by using
the axially symmetrical first and second coils 50 and 51 to be
proportional to the amount in variation in the lengths of the part,
which traversing the magnetic flux, of these coils, a sum of the
lengths of the part, which traversing the magnetic flux, of these
coils becomes constant. Thus, when moving the supporting spring 35,
the force constant (or factor) does not vary but the driving
current is proportional to the driving force exerted on the coil if
driving currents are fed through the first and second coils 50 and
51 in a direction so that the driving forces applied to these coils
have same magnitude but are exerted in opposite directions.
Next, an accessing operation of accessing the magnetic disk 47 will
be described hereinbelow by referring to FIGS. 18 and 19.
Referring to FIG. 18, when an access starting instruction is
received in a state (hereunder referred to as a track following
operation state) in which the magnetic head 37 follows a certain
track 92, driving currents are supplied through the first and
second coils 50 and 51 of the micro tracking actuator so that the
driving forces, which have an equal magnitude and are applied in
opposite directions, are exerted on the first and second coils 50
and 51. Consequently, the supporting spring 35 is fixed to the
central position.
In this state, the magnetic head 37 is moved to a target track 93
by using the main actuator 31, as illustrated in FIG. 19. Then, at
the time when the magnetic head 37 reaches a place in the vicinity
of the center of the target track 83, driving currents, whose
magnitudes are equal to one another, are fed through the coils by
reversing the direction in which the driving current flows through
one of the coils of the micro tracking actuator. At that time, the
micro tracking actuator is driven, so that the magnetic head is
made to follow the center of the target track 93. Signals
representing such driving currents are used as control signals for
setting the magnetic head 37 at the center of the target track 93
according to a position error signal obtained from the magnetic
head 37 and for causing the magnetic head 37 to follow the center
of the target track 93.
For example, a control signal for PID (Proportional plus Integral
plus Derivative) control system or a lead/lag filter adapted to
receive position error information, which is generated from the
position error signal and represents the position error between the
center of the target track 93 and the magnetic head 37, is inputted
to the micro tracking actuator to thereby casing the magnetic head
37 to follow the center of the target track 93. At that time, the
main actuator 31 is prevented from rotating or is fixed by setting
a driving current for the main actuator 31 at zero or by feeding a
minute current, which is used for coping with an external force,
therethrough. Such a minute current value is measured on-line and
is stored by making the magnetic head follow the center of the
target track 93 only by using the main actuator 31 during the micro
tracking actuator is fixed to the center position by the
aforementioned method.
During the track following operation, data is read and written by
causing the magnetic head 37 to the center of the target track 93.
During that, the track following operation is performed by feeding
driving currents through the first and second coils 50 and 51 of
the micro tracking actuator so that the driving forces have the
equal magnitudes and act in the same direction, and by utilizing
the fact that the driving current is proportional to the driving
force.
However, even when the main actuator 31 is fixed as above
described, the relative angle determined by the carriage 32 and the
supporting spring 35 varies with time owing to drift or the like.
Further, there is the possibility that the supporting spring 35
moves to a movable limit thereof when things come to the worst.
Thus, during the track following operation, there is the need for
performing a calibration operation so as to put the supporting
spring 35 to the center position. Namely, the calibration operation
is to put back the micro tracking actuator to the neutral position
by reversing the direction, in which the driving current flows
through one of the coils of the micro tracking actuator, and by
feeding the driving currents through the coils 50 and 51 by which
the driving forces exerted thereon have equal magnitudes and act in
opposite directions. In the case of this operation, the magnetic
head 37 may get out of a read/write region, which data can be read
from and written to. It is, therefore, preferable that this
operation is performed during no data is read therefrom and written
thereto. For instance, it is desirable that this operation is
performed after a predetermined time period is elapsed since the
last calibration, or during no data is read and written.
In accordance with the present invention, even when there occurs a
shift of the axis VI of symmetry, which corresponds to the first
and second coils 50 and 51, from the axis IV of symmetry, which
corresponds to the magnets 65a, 65b, 65c and 65d, a resultant force
is made to act in a direction, in which the shift is canceled or
reduced to zero, by feeding electric currents through the first and
second coils 50 and 51 in predetermined directions. Thus, during
accessing data, the relative angle between the supporting spring 35
and the carriage 32 can be fixed to a certain constant value.
Consequently, a stable accessing operation can be achieved.
Especially, the amount of variation in the length of the part,
which traverses the magnetic flux, of each of the coils is made to
be proportional to the amount of relative displacement between the
magnets 65a, 65b, 65c and 65d and the first and second coils 50 and
51 by forming the magnets 65a, 65b, 65c and 65d in such a way as to
have trapezoidal or rectangular horizontal sections and by
combining the magnets having the trapezoidal horizontal sections
with the magnets having the rectangular horizontal sections.
Furthermore, a resultant force can be made to act in a direction,
in which the supporting spring 35 rotates, on the first and second
coils 50 and 51 by reversing the electric current to be fed through
one of the coils from the state in which the supporting spring 35
is fixed. Thus, the micro tracking actuator of the present
invention can perform the functions of the conventional micro
tracking actuator by employing a physically single configuration.
Moreover, the reduction in size of the mechanism can be
achieved.
In this case, the proportional relation can be established between
the driving current and the driving force of the micro tracking
actuator. Thus, the position control of the magnetic head can be
easily achieved by the micro tracking actuator.
Consequently, the present invention can provide an excellent head
positioning mechanism for a magnetic disk device, which has
advantageous effects that cannot be obtained by the prior art, and
a drive control method therefor.
Although the preferred embodiments of the present invention have
been described above, it should be understood that the present
invention is not limited thereto and that other modifications will
be apparent to those skilled in the art without departing from the
spirit of the invention.
* * * * *